Tubing drains are known in the art and have been used to void production tubing strings of fluids produced from hydrocarbon wells using both reciprocating pumps and rotary pumps. Voiding production fluids trapped above a pump in a production tubing string is important when the pump stops because such fluids often contain sand or other contaminants that production tubing can damage the pump and/or block the production tubing if allowed to settle on top of the pump. Voiding production fluids is also important if the pump is stopped for maintenance that requires that the production tubing and the pump to be pulled from the well in order to avoid bringing uncontained and frequently contaminated hydrocarbons to the surface where they make a mess and cause pollution.
Known tubing drains have the disadvantage of requiring surface manipulation or special downhole equipment to operate them. For example, U.S. Pat. No. 4,315,542 to Dockins teaches a tubing drain that is opened or closed by rotating the production tubing at the surface.
An automatic production tubing drain for sucker rod driven progressive cavity pumps is also marketed. The automatic production tubing drain requires a special sucker rod with a lock device that must be inserted into the automatic drain when the pump is run into the well. The special sucker rod closes the tubing drain when the pump is driven and opens the tubing drain when the pump stops.
Each of these tubing drains suffers from certain disadvantages. The Dockins tubing drain will prevent pump damage and/or tubing blockage only if someone is available to open the tubing drain when the pump drive stops. The automatic drain requires the special sucker rod, and a person with the skill and knowledge to install it when the progressive cavity pump is run into the well. Furthermore, there is no known automatic tubing drain for electrically driven rotary pumps.
There therefore exists a need for an automatic tubing drain for any downhole rotary pump.